Remove confusing variable HOST.

First, HOST is always 0 in adbd, which matches ADB_HOST=0.
Second, HOST is always 1 when adb_main is called, which matches ADB_HOST=1.
For adb client that doesn't call adb_main, it never touches local_init(),
init_transport_registration() and fdevent_loop(). So the changes in adb.cpp,
services.cpp and transport_local.cpp do nothing with it.
As a conclusion, I think we can remove HOST and use ADB_HOST instead.

Change-Id: Ide0e0eca7468b6c3c130f6b50974406280678b2e
diff --git a/adb.cpp b/adb.cpp
index 821b785..1f538c0 100644
--- a/adb.cpp
+++ b/adb.cpp
@@ -55,8 +55,6 @@
 
 ADB_MUTEX_DEFINE(D_lock);
 
-int HOST = 0;
-
 #if !ADB_HOST
 const char* adb_device_banner = "device";
 static android::base::LogdLogger gLogdLogger;
@@ -416,7 +414,9 @@
     case A_SYNC:
         if(p->msg.arg0){
             send_packet(p, t);
-            if(HOST) send_connect(t);
+#if ADB_HOST
+            send_connect(t);
+#endif
         } else {
             t->connection_state = kCsOffline;
             handle_offline(t);
@@ -433,12 +433,16 @@
         t->update_version(p->msg.arg0, p->msg.arg1);
         parse_banner(reinterpret_cast<const char*>(p->data), t);
 
-        if (HOST || !auth_required) {
+#if ADB_HOST
+        handle_online(t);
+#else
+        if (!auth_required) {
             handle_online(t);
-            if (!HOST) send_connect(t);
+            send_connect(t);
         } else {
             send_auth_request(t);
         }
+#endif
         break;
 
     case A_AUTH: